This article shows before and after pictures of the lights in Japan, and is really fascinating. The "after" photo was taken the day after the earthquake/tsunami. The near total blackness on the north-eastern coast is likely mainly due to power transmission lines in the region having been snapped by the earthquake. The dimmer areas in the south-western part of Japan are likely due to voluntary power consumption by residents in those regions in order to free up electricity for the parts of the country affected by the disasters.